Graham Hutton's tutorial
on fold. Explains the universality property of fold, and its uses --
to quote Graham, "all sorts of things that every functional programmer
should know about fold". Confusomorphisms for dummies!

Courses

Stephen Gilmore's course notes on
Applicative Programming and Specification, which includes chapters by Robin
Milner, Don Sanella and others. This is a course given for post-grads at
the University of Edinburgh, and covers an introduction to ML
programming, some underlying theory, and formal program development in
`Extended ML'. 108 pages.